The 821st Strategic Aerospace Division is an inactive United States Air Force organization. Its last assignment was with Fifteenth Air Force at Ellsworth Air Force Base, South Dakota, where it was inactivated on 30 June 1971.

The division was activated as the 821st Air Division at Ellsworth in 1959 to command Boeing B-52 Stratofortress units of Strategic Air Command (SAC), which had been dispersed along the northern border of the United States to reduce their vulnerability to Soviet missile attacks.

In 1962, the 44th Strategic Missile Wing was activated at Ellsworth and assigned to the division along with a second Minuteman missile wing in Montana. At the same time, the B-52 wings formerly assigned to the division were transferred, except for the 28th Bombardment Wing at Ellsworth. The division's units assumed a heightened alert role during the Cuban Missile Crisis, including the first SAC LGM-30A Minuteman I to be put on alert.

The division continued at Ellsworth until June 1971, when SAC organized its divisions on a weapons system basis, and its bombardment and missile wings were reassigned to different divisions.

Starting in 1957, the 28th Bombardment Wing at Ellsworth Air Force Base began to upgrade from the Convair B-36 Peacemaker to the Boeing B-52 Stratofortress. However, Strategic Air Command (SAC) was concerned that bases with large concentrations of the new jet bombers made attractive targets. SAC's response was to break up its B-52 wings and scatter their aircraft over a larger number of bases, thus making it more difficult for the Soviet Union to knock out the entire fleet with a surprise first strike. At the same time, the reduced number of interceptors available to Air Defense Command (ADC) due to attrition and closing production lines made ADC bases along the northern tier of states available for expansion to accommodate SAC heavy bombers and tankers. In 1958 SAC established strategic wings at Grand Forks Air Force Base, North Dakota, Minot Air Force Base, North Dakota, and Glasgow Air Force Base, Montana, all ADC bases. The 821st Air Division was activated at Ellsworth in January 1959 to command these new strategic wings and the 28th Wing at Ellsworth.

However, the establishment of wings did not immediately disperse the bomber force. It would be 1960 before the 28th Wing's 717th and 718th Bombardment Squadrons were transferred from Ellsworth to other bases. Although Boeing KC-135 Stratotankers were assigned earlier, Minot and Glasgow only received their bombers in 1961 and the Grand Forks wing only activated its bomber squadron in 1962. As their squadrons became combat ready, one third of each wing's aircraft were maintained on fifteen-minute alert, fully fueled, armed and ready for combat to reduce vulnerability to a Soviet missile strike. This was increased to half their aircraft in 1962.

In December 1960, the division added an intercontinental ballistic missile squadron to its strike forces, when the 850th Strategic Missile Squadron was activated and assigned to the 28th Bombardment Wing as an HGM-25A Titan I squadron. However, the squadron never became operational while assigned to the 28th.

1962 was a year of change for the division's responsibilities. On 1 January, the 44th Strategic Missile Wing was activated at Ellsworth and assigned to the 821st. The 850th Strategic Missile Squadron was assigned to the new wing. The same day, the division assumed support responsibility for Ellsworth through its 821st Combat Support Group. The following month, the division became the 821st Strategic Aerospace Division when SAC added the term "aerospace" to the names of its units with both bomber and missile strike elements.